Method and composition for suppressing the nitrification of ammonium nitrogen present in soil



United States Patent fiiice with K sti-exited Qec. 5, 1961 METHOD ANDCOMPOSITEON FDR SUPPRESSTNG TIE NITREFICATEGN F AMMONTUM NITRG- GENPRESENT IN 0IL Cleve A. 1. Goring, Garden Grove, Calif, assignor to TheDow Chemicai Company, Midland, Mich, a corporation of Delaware NoDrawing. Filed Apr. 16, 1957, Ser. No. 653,066

9 Claims. (Cl. 711) The present invention relates to the culture ofcrops and is particularly concerned with a new agronomical practice andcomposition for conserving soil nitrogen and for supplying the soilnitrogen requirements for plant nutrition.

Since the majority of plants obtain most or all of their nitrogenrequirements from the soil, the adequate provision of nutrient nitrogenin soil for plant growth is one of the foremost agronomic problems. Thenitrogen in the soil is found to occur primarily in three forms: organicnitrogen, ammonium nitrogen and nitrate nitrogen, of which ammoniumnitrogen and nitrate nitrogen are the primary forms utilized by plants.This nitrogen is absorbed by plants in solution from the soil in theform of ammonium ions and nitrate ions.

The organic nitrogen in the soil consists of a large number of compoundsand originates from manure, crop residues, organic fertilizers orbacterial syntheses. Since with the exception of the organic reducednitrogen fertilizers such as urea, the solubility of these compounds inwater is very low, they are neither readily leached from the soil nordirectly available to the plants for use. In order to be available tothe plants, the nitrogen in the organic compounds must be converted bysoil bacteria to ammonia or inorganic ammonium salt This conversion,when from organic reduced nitrogen fertilizers such as urea, takes placevery rapidly, while the conversion and breakdown of the other organicnitrogen compounds takes place very slowly. Following the conversion,the ammonium nitrogen is very rapidly oxidized by soil bacteria toinorganic nitrate nitrogen. In this process, the ammonium nitrogen isfirst oxidized to the intermediate nitrite nitrogen which is thenrapidly oxidized to nitrate n trogen. This mineralization of organicnitrogen constantly replenishes the soil with nitrogen available forplant absorption.

The ammonium-nitrogen in the soil is derived from bacterial conversionof organic nitrogen or from the added reduced nitrogen fertilizers suchas anhydrous ammonia, aqueous ammonia, ammonium phosphate, ammoniumnitrate and ammonium sulfate. These ammonium compounds or inorganicreduced nitrogen compounds are readily soluble in water or aqueous soilmedium. When in solution, the reduced nitrogen occurs largely as theammonium ion. Due to the cationic nature of this ion, the ion isstrongly adsorbed on the soil colloids or base exchange complex of thesoil. This colloidal-bound ammonium nitrogen exists in equilibrium witha small concentration of ammonium ions in the soil solution. Thus, thecolloidal-bound ammonium nitrogen provides a dynamic nitrogen reservoirto maintain a supply of ammonium ions in the soil solution for plantadsorption. Further, since the ammonium nitro gen in the soil occursprincipally as colloidal-bound nitrogen, only very small quantities ofthe ammonium form of soil nitrogen are lost from the feeding zone of theplants by leaching.

The nitrate nitrogen in the soil is derived from the oxidation ornitrification of ammonium nitrogen by soil bacteria, or by the additionof inorganic nitrate fertilizers such as ammonium nitrate, sodiumnitrate, potassium nitrate and calcium nitrate. The inorganic nitratecompounds are readily soluble in water and the aqueous soil medium. Whenso dissolved, the nitrate nitrogen largely exists as the nitrate ion.Because of the anionic nature of this ion, nitrate nitrogen is notadsorbed by soil colloids. Accordingly, the nitrate nitrogen is rapidlyleached by rainfall and irrigation and readily lost from the feedingzone of the plants. Further, the nitrate nitrogen is reduced by manysoil bacteria to nitrogen gas. The latter process is known asdenitrification and accounts for an additional loss of large quantitiesof nitrate nitrogen from the soil. The yearly loss from leaching anddenitrification amounts to from 20 to percent of the nitrate nitrogenfound in the soil, whatever its source.

Nitrification or the conversion of the ammonium nitrogen in soil tonitrate nitrogen by bacteria action occurs at a rate which is dependentprimarily upon the soil temperature and the soil pH. The rate is alsosome- What dependent upon the type of soil and the moisture content ofthe soil. The rate of nitrification is rapid when the soil temperatureis at least 10 C. and the soil pH is at least 5. For example, theconversion of ammonium nitrogen to nitrate nitrogen in sand, silt orclay loam soil having a pH of at least 6 may take place at a rate offrom 20 pounds of nitrate nitrogen per acre per week at 10 (3., to 500pounds of nitrate nitrogen per acre per Week at 35 C. Even attemperatures as low as 2 C., nitrification will oftentimes occur in suchsoils at a rate of 25 pounds of nitrate nitrogen per month. Thus,ammonium nitrogen is very rapidly changed to nitrate nitrogen in mostagricultural soils.

The tremendous losses of soil nitrogen resulting from the rapidnitrification of ammonium nitrogen, and the leaching and bacterialdecomposition of nitrate nitrogen have depleted many agricultural soilsof the nitrogen reserves and nitrogen requirements for plant nutrition.In order to replenish the soil nitrogen, the agriculturalist hasresorted to the use of large amounts of nitrate fertilizers and reducednitrogen fertilizers. In many instances, multiple fertilizer treatmentsduring the growing season have been required to maintain adequatenitrogen requirements for plant growth. In this practice, the greaterproportion of the employed fertilizers is in the form of reducednitrogen fertilizers. By the expression reduced nitrogen fertilizers ismeant fertilizers containing nitrogen in the reduced state and isinclusive of ammonium salts, ammonia, and water-soluble organiccompounds readily convertible in soil to ammonia or ammonium ions suchas urea and cyanamide.

Since the nitrogen must be present as nitrate nitrogen beforesubstantial quantities can be leached from the soil or lost bydenitrification, the application of nitrogen as reduced nitrogenfertilizers provides the agriculturalist with a short interval duringwhich available reduced nitrogen is at a maximum and conditions forleaching and denitrification are at a minimum. This interval isparticularly advantageous during the initial growth of seeds andemerging seedlings when high soil nitrogen concentrations are verydesirable. In addition, the armmonium nitrogen absorbed by plants isimmediately available for assimilation into organic materials beingsynthesized thereby. In contrast, the nitrate nitrogen must be reducedbefore it can be assimilated in the synthesis of plant materials. Thisreduction is carried out in the plant usually at the expense ofsynthesized carbohydrate. Although so-me plants seem to do well oneither ammonium nitrogen or nitrate nitrogen as a source of nitrogennutrients, many plants such as potato, corn, rice, buckwheat, pineapple,cotton and orange prefer ammonium nitrogen and appear to grow best inthe presence of substantial amounts of this form of nitrogen. Thus, theneed for a method of suppressing the rapid loss of soil nitrogen is wellrecognized by agriculturalists.

An object of the present invention is to provide a new and improvedagronomic practice for conserving soil nitrogen. A further object is theprovision of a new and improved method for suppressing the loss of soilnitrogen. An additional object is the provision of a new and improvedmethod for suppressing the loss of ammonium nitrogen from soil. Anotherobject is the provision of a new and improved method for supplying soilwith nitrogen available for plant growth. Another object is theprovision of a new and improved method for suppressing the. loss ofreduced nitrogen fertilizer supplements from soil. A further object isthe provision of a new and improved method for suppressing the loss ofammonium ions from soil. An additional object is the provision of a newand improved method for suppressing the nitrification of ammoniumnitrogen in soil. Another object is the pro- 7 vision of a new andimproved method for suppressing wherein X represents chlorine orbromine; and (2) salts of said halopyridines. Suitable salts includehydrochlon'des, hydrobromides, nitrates, oxalates, phosphates, sulfatesand formates. The halopyridine compounds are oily liquids or crystallinesolids adapted to be readily and conveniently distributed in the soil.

By the practice of this invention, the nitrification of ammoniumnitrogen in the soil to nitrate nitrogen is suppressed therebypreventing the rapid loss of ammonium nitrogen from the soil.Furthermore, by proper distribution of the halopyridine compound, thisaction of inhibiting the transformation of ammonium nitrogen to nitratenitrogenis effective over a prolonged period of time. The ammoniumnitrogen may arise from added ammonium nitrogen fertilizers or be formedin the soil by conversion of the organic nitrogen constituents found insoil or added thereto as components of organic fertilizers.

The provision of an effective dosage of the halopyridine compound in thesoil or growth medium is essential for the practice of the presentinvention. In general, good results are obtained when the growth mediumis modified with the halopyridinecompound in the amount or" from 2 to150 parts or more by weight of the latter per million parts by weight ofgrowth medium. in field applications, the halopyridine compound may bedistributed in the soil in the amount of at least 0.5 pound per acre andthrough such a cross-section of the soil as to provide for the presencetherein of an effective concentration of the agent. It is usuallypreferred that the halopyridine compound be distributed to a depth of atleast 0.7 pound per acre inch of soil. By dispersing very large dosagesin growth media, a prolonged inhibition of nitrification may be obtainedover a period of many months. The concentration of the activehalopyridine compound is eventually reduced'to a minimum bydecomposition in the soil.

In one embodiment of the present invention, the halopyridine compound isdistributed throughout the growth media prior to seeding ortransplanting the desired crop plant.

In another embodiment, the soil in the root zone of growing plants istreated with the halopyridine compound in an amount effective to inhibitnitrification but sublethal to plant growth. In such operations, thehalopyridine compound should be supplied in the soil in an amount nogreater than about 50 parts by weight per million parts by weight of thesoil. By following such practice, no adverse eifect is exerted by thehalopyridine compound upon growth of seeds or plants. O'ftentimes it isdesirable to treat the soil adjacent to plants, and this procedure maybe carried out conveniently in side-dressing operations.

In a further embodiment, soil may be treated with the halopyridinecompound following harvest or after fallowing to prevent rapid loss ofammonium nitrogen and to build up the ammonium nitrogen formed byconversion of organic nitrogen compounds. Such pracitce conserves thesoil nitrogen for the following growing season.

In an additional embodiment, the soil is treated with the halopyridinecompound in conjunction with the ap plication of reduced nitrogenfertilizers. The treatment with the halopyridine compound may be carriedout prior to, subsequent to or simultaneously with the application offertilizers. Such practice prevents the rapid loss of the ammoniumnitrogen added as fertilizer and the ammonium nitrogen formed from theorganic reduced nitrogen in fertilizers by the action of soil bacteria.The administration to the soil of the halopyridine compound as aconstituent of an ammonium nitrogen fertilizer composition constitutes apreferred embodiment of the present invention.

The present invention may be carried out by distributing thehalopyridine compound in an unmodified form through growth medium. Thepresent method also embraces distributing the compound as a constituentin liquid or finely dividedsolid. compositions. In such practice, thehalopyridinecompound may be modified with one or more additaments orsoil treating adjuvants including water, petroleum distillates or otherliquid carriers, surface-active dispersing agents, finely divided inertsolids and nitrogen fertilizers. Depending upon the concentration of thehalopyridine compound, such augmented composition may bedistributed inthe soil without further modification or be considered a concentrate andsubsequently dilutedwith additional inert carrier to produce theultimate treating composition. The required amount of the halopyridinecompound may be supplied to growth media in from 1 to 50 gallons oforganic solvent carrier, in from 5 to 27,000 or more gallons of aqueouscarrier or in from about 20 to 2,000 pounds of solid carrier per acretreated. When an organic solvent carrier is employed, it may be furtherdispersed in the above volume of aqueous liquid carrier.

The concentration of the halopyridine compound in compositions to beemployed for the treatment of growth media is not critical and may varyconsiderably provided the required dosage of effective agent is suppliedto the growth media. The concentration of the halopyridine compound mayvary from 0.001 percent by weight to percent by weight of thecomposition, depending on whether the composition is a treatingcomposition or a concentrate composition and whether it is in the formof a solid or a liquid. In aqueous liquid treating compositions,concentrations of from 0.001 percent to 0.25 percent by weight of thehalopyridinecompound is considered the preferred composition. Theconcentration of the halopyridine compound in organic solvents may befrom 2.0 to 50 percent by weight. Concentrate liquid compositionsgenerally contain from 2.5 to 50 percent by weight of the halopyridinecompound. Solid compositions may contain the halopyridine compound inamounts as high as 95 percent by weight of the active compound. Treatingcompositions generally contain 0.004 percent to 10 percent by weight ofthe halopyridine compound. Concentrate compositions oftentimes maycontain from 2.5 to 95 percent of the halopyridine compound.

Liquid compositions containing the desired amount of the halopyridinecompound may be prepared by dispersing the latter in one or more liquidcarriers such as water or an organic solvent, with or without the aid ofa suitable surface-active dispersing agent or emulsifying agent.Suitable organic solvents include acetone, diisobutylketone, methanol,ethanol, isopropyl alcohol, diethyl ether, toluene, methylene chloride,chlorobenzene and the petroleum distillates. The preferred organicsolvents are those which are of such volatility that they leave littlepermanent residue in the soil. When the solutions of the halopyridinecompound in organic solvents are to be further diluted to produceaqueous dispersions, the preferred solvents include acetone and thealcohols. When the liquid carrier is entirely organic in nature,particularly desirable carriers are the petroleum distillates boilingalmost entirely under 400 F. at atmospheric pressure and having a flashpoint above about 80 F. Dispersing and emulsifying agents which may beemployed in liquid compositions include condensation products ofalkylene oxides with phenols and organic acids, alkyl aryl sulfonates,polyoxyalkylene derivatives of sorbitan esters, complex ether alcohols,mahogany soaps and the like. The surface-active agents are generallyemployed in the amount of from 1 to 20 percent by weight of thehalopyridine compound.

Solid compositions containing the active halopyridine compound may beprepared by dispersing the latter in finely divided inert solid carrierssuch as talc, chalk, gypsum, vermiculite, bentonite and the like,fullers earth, attapulgite and other clays, various solid detergentdispersing agents and solid fertilizer compositions. In preparing suchcompositions, the carrier is mechanically ground with the halopyridinecompound or wet with a solution or dispersion thereof in a volatileorganic solvent. Depending upon the proportions of ingredients, thesecom positions may be employed without further modification or beconsidered concentrates and subsequently further diluted with solidsurface-active dispersing agent, talc, chalk, gypsum or the like toobtain the desired treating composition. Furthermore, such concentratecompositions may be dispersed in water with or without added dispersingagent or agents to prepare aqueous soil treating compositions.

Soil treatment compositions may be prepared by dispersing thehalopyridine compound in fertilizers such as ammonium fertilizer ororganic nitrogen fertilizer. The resulting fertilizer composition may beemployed as such or may be modified as by dilution with additionnitrogen fertilizer or With inert solid carrier to obtain a compositioncontaining the desired amount of halopyridine compound for treatment ofsoil. Further, an aqueous dispersion of the halopyridinecompound-fertilizer composition may be prepared and administered to thegrowth medium. Fertilizer compositions comprising the halopyridinecompound in intimate admixture with ammonium fertilizers constitutepreferred embodiments of the present invention.

In fertilizer compositions comprising a reduced nitrogen fertilizer, itis desirable that the halopyridine compound be present in an amount ofat least 0.5 percent by weight based on the weight of the nitrogenpresent in the fertilizer as reduced nitrogen. Thus, when a fertilizercomposition contains both reduced nitrogen and other forms of nitrogensuch as in the case of ammonium nitrate fertilizer compositions, theamount of halopyridine compound is based on the Weight of nitrogenpresent in the ammonium component.

In operations carried out in accordance with the present invention, thesoil may be impregnated in any convenient fashion with the halopyridinecompound or a composition containing these agents. For example, thesemodified or unmodified compositions may be mechanically mixed with thesoil; applied to the surface of soil and thereafter dragged or discedinto the soil to a desired depth; or transported into the soil with aliquid carrier such as by injection, spraying or irrigation. When thedistribution is carried out by introducing the halopyridine compound inthe water employedto irrigate the soil, the amount of water is varied inaccordance with the moisture content of the soil in order to obtain adistribution of the halopyridine compound to the desired depth. Thehalopyridine compound may be readily and conveniently distributed to adepth of from two to four feet by irrigation methods. The preferredmethods embrace procedures using any of these steps or combination ofsteps wherein the halopyridine compound is distributed in the soilsubstantially simultaneously with a reduced nitrogen fertilizer.

The following examples illustrate the invention but are not to beconstrued as limiting.

EXAMPLE 1 An aqueous ammonium fertilizer composition containing 500parts by weight of nitrogen and 50 parts by weight of Z-chloropyridineper million parts of aqueous mdium was prepared by dispersing a 4percent (weight by volume of solvent) acetone solution of2-chloropyn'dine in aqueous ammonium sulfate solution. (The amount ofnitrogen in all examples is based on the nitrogen present in thefertilizer in the reduced form.)

The composition so prepared was employed to treat seed beds of sandyloam soil having a pH of about 8, containing essentially no organicmaterial and having been freed of nitrite and nitrate nitrogen by priorthorough leaching with water. In the treating operation, the compositionwas applied to the seed beds as a soil drench, and the soil in the bedsthoroughly mixed to insure a substantially uniform distribution of thecomposition throughout the soil. The amount of composition employed wassufficient to supply parts by Weight of nitrogen and 10 parts by Weightof Z-chloropyridine per million parts by weight of soil. In a checkoperation, other seed beds similarly prepared were fertilized with asimilar aqueous fertilizer composition containing the same amount ofacetone and arnmonium sulfate but omitting the halopyridine compound.The composition was applied in an amount sufficient to supply the sameconcentration of nitrogen to the soil as the treating compositioncontaining Z-chloropyridine. The soil temperature of all seed beds wasmaintained at about 70 F. for the period of the determination.

At various intervals following treatment, samples of soil were takenfrom the different seed beds and the extent of nitrification of theadded ammonium sulfate fertilizer determined by analyses for combinednitrate plus nitrite nitrogen. The determinations were carried out byextracting the nitrate and nitrite from the soil With a saturatedcalcium sulfate solution, developing color in the clear supernatant ofthe extract with diphenylamine in sulfuric acid, and comparing the colorwith a standard solution containing known concentrations of nitrate andnitrite ions. This procedure is similar to that described inColorimetric Methods of Analysis by F. D. Snell and C. T. Snell, D.VanNostrand Company, Inc., volume II, 3rd Edition, page 8 01.

The percent nitrification in the seed beds of the added ammonium sulfateat various intervals is set forth in the following table:

7 E A PLE 2 Experiments were carried out in a manner similar tQ thatdescribed in Example 1 but wherein the final con: centrations of the2-chloropyridine were greatly reduced. Aqueous ammonium fertilizercompositions contained 500 parts by weight of nitrogen and 25 and 10parts by weight, respectively, of 2-chloropyridine per million parts ofaquous media. These were prepared by dispersing a 2 percent (weight byvolume of solvent) acetone solution of 2-chloropyridine in aqueousammonium sulfate solution. The compositions were applied to soil seedbeds in amounts suificient to give a concentration of nitrogen thereinof 100 parts by weight and of 2-cliloro pyridine therein of 5 parts and2 parts by weightv per million parts by weight of soil, respectively.The degree of nitrification when determined after an interval of 6 dayswas found to be percent and percent, respectively, and after 13 days 0percent and 15 percent, re-

spectively. A check operation carried out with a composition containingno 2-chloropyridine showed 100 percent nitrification at both intervals.

EXAMPLE 3 An experiment was carried out in a manner similar to thatdescribed in Example 1 but wherein 2-bromopyridine was substituted for2-chloropyridine and the final concentration of the halopyridine in thesoil was reduced to 2 parts by weight per million parts by weight ofsoil. The amount of nitrogen applied to the soil was the same, i.e., anamount sufficient to supply 100 parts by weight per million parts byweight of soil. The degree of nitrification was determined afterintervals of 7 and 14 days and found to be 5 and 10 percent,respectively. A check operation carried out with a compositioncontaining no Z-bromopyridine showed 100 percent nitrification atboth intervals.

EXAMPLE 4 Concentrate compositions are prepared as follows:

(A) parts by weight of Z-chloropyridine-hydrochloride, 65 parts ofxyleneand 10 parts of an alkylated aryl polyether alcohol (Triton X-lOO)are mechanically mixed together to obtain an emulsifiable liquidcomposition.

(B) 90 parts by weight of 2-bromopyridine-hydrobromide and 10 parts ofan alkyl aryl sulfonate (Acto 700) are mechanically mixed together toobtain a water-dispersible mixture.

These compositions may be dispersed in water to produce aqueouscompositions having desirable wetting and penetrating properties. Theseaqueous compositions are then employed to treat soil in an amountsufficient to distribute the halopyridine compound therein in effectiveconcentrations. The concentrates may also be dispersed in aqua ammoniato prepare fertilizer compositions.

EXAM E weight of the Z-bromopyridine salt.

(C) Z-brOmopyridine is mechanically mixed with urea to prepare a reducednitrogen fertilizer composition containing 2 percent by weight of2-bromopyridine.

These fertilizer compositions are distributed in soil to supply thenitrogen requirements for plant nutrition. The treated soil is resistantto nitrification and provides nitrogen available for plant growth over aprolonged period .of time.

8 EXAMPLE 6 Aqueous ammonium fertilizer compositions containing 1,000parts by weight of nitrogen and 50 parts by weight of 2-chloropyridinein a million parts of aqueous media were prepared by dispersing anacetone solution containing 4 percent (weight by volume of solvent) of2- chloropyridine in aqueous solutions of various ammonium compounds.

In an operation similar to that described in Example 1, the soil in seedbeds was treated with the above described compositions to distribute aparticular composition throughout the soil in an amount sufficient tosupply a concentration of nitrogen in the soil of 200 parts by weightand of 2-chloro'pyridine of 10 parts by weight per million parts byweight of soil. The treated soil was maintained at F. for the period ofthe determination. At various intervals, samples of the soil were takenand analyses made to determine the extent of nitrification.

Soils treated with the ammonium phosphates and aqua ammonia wereanalyzed for nitrate "plus nitrite nitrogen as previously described. Thesoils treated with ammonium nitrate were analyzed for residual ammoniaby extracting the soil with 2 molar potassium chloride and the ammoniainthe extract determined by comparisons with a standard on a spot plateusing Nesslers reagent as indicator.

Check operations were simultaneously carried out on other seed bedsemploying similar aqueous fertilizer compositions but containing no2-chloropyridine. The results of the treating check operations are givenin Table II.

Table II Interval Percent Treating Composition Following N itrifi-Treatment cation In Days Ammonium nitrate+2-chloropyridine 1 4 0Ammonium nitrate (check) .Q 14 S0 Ammonium nitrate+2-ehloropyridine 20 0Ammonium nitrate (check). 20 Aqua arnrnonia-i-Z-ohlowpyfidine 14 15 Aquaammonia (check) i. 14 100 Diammoniuui ph0sphate+2-ehl0ro 1'4 10Diammonium phosphate (check) 14 100 Monoammonium phosphate+2chloropyridine 40 25 hlionoammonium phosphate (check) 1 40 100Monoammonium phosphate+2 ehloropyri- (lino 48 38 Monoammouium phosphate(check). 7 48 100 EXAMPLE 7 A solid fertilizer composition was preparedas follows: (1) an inhibitor component was prepared by (q) mixing andgrinding together 0.2 gram of 2-bromopyridine and r m of pn e d i -5 mst py ophyllite thereto and grinding the resulting mixture until a finelypowdered uniform composition was obtained; (2) a fertilizer componentwas prepared by hammermilling together a 50:50 mixture by weight ofammonium sulfate and pyrophyllite to obtain a fine uniform composition;(3 the inhibitor component and fertilizer component were mixed togetherin various ratios on a roller mill to obtain soil treating compositionscontaining 2-bromopyridine in varying concentrations expressed inpercent based on the nitrogen in the compositions. These compositionswere employed to fertilize various beds of sandy loam soil containingessentially no organic material and having a pH of about 8. The soilemployed had been previously leached to remove all nitrate and nitritenitrogen constituents. A sufficient amountof water was added to thevarious beds to give the soil in the beds varying moisture content. Thebeds were fertilized in areas to be planted by providing depressions andadding thereto the fertilizer treating composition and then covering thecomposition with soil. The amount of composition employed was sufficientto supply parts by weight ofnitrogen per million parts by weight ofsoil. The soil was maintained in the temperature range of from 70 to 85F. for three weeks. At the end of this period, samples of soil wereanalyzed for content of nitrate plus nitrite nitrogen to determine theextent of nitrification of the added ammonium sulfate. The results werecompared with check determinations wherein no 2-brornopyridine was addedto the fertilizer composition. The results obtained are given in TableIII.

Irrigation water was modified by adding an acetone solution containing 5percent (weight by volume of solvent) of Z-chloropyn'dine to give aconcentration of the halopyridine therein of 50 parts by weight in amillion parts of water.

The water modified as described above was employed to irrigate dry sandyloam soil having a pH of 8 and previously leached to remove any nitriteand nitrate present. The depth of the sandy loam bed was 2021 inches. Anamount of modified water equal to 6 acres inches per acre of soil wasadded and allowed to equilibrate in the soil by standing for severaldays. At the end of this period, samples of soil from various depthswere taken. To each sample a sufiicient volume of an aqueous ammoniumsulfate solution containing 2,500 parts of nitrogen by weight permillion parts of water Was added to give a composition containing 100parts by weight of nitrogen per million parts of soil. The fertilizedsoil samples were thereafter maintained in the temperature range of from70 to 85 F. At periodic intervals, samples of the soil were taken andanalyses made on the nitrate plus nitrite nitrogen to determine theextent of nitrification. The results were given in Table IV.

A check operation was carried out by irrigating soil with unmodifiedwater. In determinations made on various layers of soil of the checkoperation it was found that after 9 days there was 100 percentnitrification at all depths in the soil.

EXAMPLE 9 An aqueous soil treating composition containing 100 parts byweight of Z-chloropyridine, 1,000 parts by weight of nitrogen asammonium sulfate and 500 parts by weight of phosphorus as phosphoricacid was prepared by dispersing a 4 percent (weight per volume ofsolvent) acetone solution of 2-chloropyridine into an aqueous solutionof ammonium sulfate and phosphoric acid.

Pots were prepared for planting with 500 grams of sandy loam soil havinga pH of 8 and a 4 percent moisture content. 200 milliliters of thetreating composition prepared as described above was poured over thesoil (an amount equal to about 1 inch of liquid) to supply to the soilZ-chloropyridine in an amount sufficient to give a concentration of 40parts by weight per million parts by weight of soil and a concentrationof nitrogen of 400 parts per million. The treated soil was then coveredwith paper to reduce evaporation and maintained in the temperature rangeof from 70 to F.

After a period of six weeks, the soil in the pots was leached with 6inches of water and thereafter planted with three species. Each pot wasplanted with four tomato plants, five milo plants and a thick stand ofrye. After an appropriate growth interval, the tops of the plants wereharvested just above ground level and weighed. The average fresh weightin grams per pot was determined at the time of harvest which was 35 daysfor tomato plants, 46 days for milo plants and 47 days for rye plants.

A check operation was carried out simultaneously wherein soil .in potswas similarly fertilized with a composition containing the same amountof ammonium sulfate, phosphoric acid and acetone but no2-chloropyridine.

The weights of the plant tops at harvest in both the treating and checkoperations are set forth in Table V.

1. A method for suppressing the nitrification of ammonium nitrogenpresent in soil and preventing rapid loss of ammonium nitrogen therefromwhich comprises impregnating soil below the soil surface in the growingarea thereof in concentration sufficient to suppress nitrification, witha halopyridine compound, said halopyridine compound being selected fromthe group consisting of (1) halopyridines having the formula wherein Xrepresents a member of the group consisting of chlorine and bromine; and(2) salts of said halopyridines, said concentration being from about 2to parts by weight per million parts by weight of soil.

2. A method according to claim 1 wherein the halopyridine compound is2-chloropyridine.

-3. A method according to claim 1 wherein the halo pyridine compound is2-bromcpyridine.

4. A method according to claim 1 wherein the halopyridine compound isadded in an amount sufficient to give a concentration in the soil offrom 2 to 50 parts by Weight per million parts by weight of soil.

6. A method according to claim 4 wherein the halopyridine compound isintroduced in the soil at a point near the roots of the growing plants.

6. A method for treating soil to inhibit the conversion therein ofammonium nitrogen to nitrate and nitrate nitrogen and to prevent rapidloss of ammonium nitrogen from soil which comprises impregnating thesoil below the soil surface in the growing area of the soil in an amountsuflicient to inhibit nitrification with a composition comprising ahalopyridine compound in intimate admixture with a soil treatingadjuvant, the halopyridine compound being selected from the groupconsisting of (1) halopyridines having the formula Ny X wherein Xrepresents a member of the group consisting of chlorine and bromine, and(2) salts of said halopyridines and the impre nationbeing so carried outas to provide a concentration in soil of at least 2 parts by weight ofhalopyridine compound per million parts by weight of soil.

7. A method according to claim 6 wherein the adjuvant is a reducednitrogen fertilizer composition wherein said reduced nitrogen fertilizeris a fertilizer selected 7 from the group consisting of ammonia,ammonium salts and urea. V

8. A fertilizer composition comprising a major amount of a reducednitrogen fertilizer as source of ammonium ions and a halopyridinecompound selected from the group consisting of (l) halopyridines havingthe formula wherein X represents a member of the group consisting ofchlorine and bromine, and (2) salts of said halopyridines; and whereinthe halopyridine compound is present in a concentration of at least 0.5percent by weight based on the weight of reduced nitrogen present in thefertilizer, and wherein said reduced nitrogen fertilizer is selectedfrom the group consisting of ammonia, ammonium salts and urea.

9. A fertilizer composition comprising a major amount of nitrogenfertilizer as source of ammonium ions and 2-chloropyridine as thehaiopyridine compound wherein said halopyridine compound is present in aconcentration of at least 0.5 percent by weight based on the weight ofthe reduced nitrogen present in the fertilizer, and wherein said reducednitrogen fertilizer is a fertilizer selected from the group consistingof ammonia, ammonium salts and urea.

References Qited in the file of this patent UNITED STATES PATENTS2,312,801 Craig et al. Mar. 2, 1943 2,314,091 Jones Mar. 16, 19432,620,266 Schlesinger et a1 Dec. 2, 1952 2,679,453 Brett et a1. May 25,1954

